Everything Science Grade 10

4.6 CHAPTER 4. THE ATOM

2 .Fluorine

Fluorine (F) has an atomic number

of 9 , meaning that a neutral atom

also has 9 electrons. The first 2 elec-

trons are found in the first energy

level, while the other 7 are found in

the second energy level (Figure 4.7).

Figure 4.7: Electron arrangement of a fluorine atom.

3 .Neon

Neon (Ne) has an atomic number of

10 , meaning that a neutral atom also

has 10 electrons. The first 2 elec-

trons are found in the first energy

level and the last 8 are found in the

second energy level. (Figure 4.8).

Figure 4.8: Electron arrangement of a neon atom.

But the situation is slightly more complicated than this. Within each energy level, the

electrons move inorbitals. An orbital defines the spaces or regions where electrons move.

DEFINITION: Atomic orbital

An atomic orbital is the region in which an electron may be found around a

single atom.

The first energy level contains only one s orbital, the second energy level contains one s

orbital and three p orbitals and the third energy level contains one s orbital and three p

orbitals (as well as five d orbitals). Within each energy level, the s orbital is at a lower

energy than the p orbitals. This arrangement is shown in Figure 4.9.

Note

Each block in fig-
ure 4.9 is able to hold
two electrons. This
means that the s or-
bital can hold two
electrons, while the
p orbital can hold a
total of six electrons,
two in each of the
three blocks.

This diagram also helps us when we are working out the electron configuration of an

element. The electron configuration of an element is the arrangement of the electrons in the

shells and subshells. There are a few guidelines for working out the electron configuration.

These are:

• Each orbital can only holdtwo electrons. Electrons that occur together in an orbital
  are called anelectron pair.


• An electron will always try to enter an orbital with the lowest possible energy.

80 Chemistry: Matter and Materials